Apparatus for cleaning glass substrate for use in information recording medium

ABSTRACT

An apparatus for cleaning a glass substrate for use in information recording medium, having improved detergency, includes a plurality of gas feeding pipes, provided in a cleaning tank storing therein a cleaning fluid, for feeding air into the cleaning tank to generate bubbles of air in the cleaning fluid in which a glass substrate is immersed. The bubbles are brought into contact with the glass substrate while stirring the cleaning fluid to effectively remove deposits on the surface of the glass substrate.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an apparatus for cleaning a glass substrate, and more particularly to an apparatus for cleaning a glass substrate for use in information recording medium, such as a magnetic disk, a magneto-optical disk, or an optical disk.

[0002] A glass substrate for use in information recording medium has been formed by a process in which a sheet-form untreated glass plate is cut into a disk form, and the surface of the resultant untreated glass plate is polished and subjected to chemically reinforcing treatment. In the chemically reinforcing treatment, the untreated glass plate is immersed in a heated chemically reinforcing treatment solution so that monovalent metal ions contained in the glass plate are replaced by monovalent metal ions having a larger ionic radius. After the chemically reinforcing treatment, the resultant glass substrate is taken out from the chemically reinforcing treatment apparatus, and cooled to around room temperature. At this moment, a molten salt formed from the monovalent metal ions replaced and released out of the glass is deposited on the surface of the glass substrate. Deposits on the glass substrate include fine particles, such as metallic particles mixed into the molten salt, dust, an abrasive material, or abrasive powder. Therefore, for removing such deposits from the surface of the glass substrate, the glass substrate is subjected to cleaning treatment after the chemically reinforcing treatment.

[0003] An apparatus for cleaning a glass substrate has a cleaning tank having an opening formed in the top surface. The glass substrate after being subjected to the chemically reinforcing treatment is immersed in the cleaning fluid stored in the cleaning tank. A water warming heater for heating the cleaning water to 30 to 100° C. is provided inside or outside the cleaning tank. Further, an ultrasonic wave generator for irradiating the glass substrate with ultrasonic waves to pulverize deposits on the surface of the glass substrate is provided in the cleaning tank. The deposits pulverized leave the surface of the glass substrate and are dissolved in the warm water due to the polarity and heat energy of the warm water, and thus removed.

[0004] In a conventional cleaning apparatus, the deposits pulverized, especially molten salts are dispersed only in the vicinity of the glass substrate and then dissolved. Therefore, as dissolution of the salts proceeds, the dissolution rate of the molten salt is drastically lowered, so that the cleaning apparatus cannot exhibit a satisfactory detergency.

[0005] Further, the deposits contain fine particles insoluble in warm water. Such fine particles are dispersed in the vicinity of the glass substrate during irradiation of ultrasonic waves, but they are possibly deposited again on the surface of the glass substrate after irradiation of the ultrasonic waves is stopped. In this case, the cleanliness of the surface of the glass substrate lowers, so that micro-protrusions are formed on the surface, resulting in deterioration of the smoothness of the glass substrate.

[0006] In addition, when the amount of glass substrates treated per operation is increased, the efficiency of removing deposits by ultrasonic waves is lowered.

SUMMARY OF THE INVENTION

[0007] An object of the present invention is to provide an apparatus for cleaning a glass substrate for use in information recording medium, having improved detergency.

[0008] In one aspect of the present invention, an apparatus for cleaning a glass substrate for use in information recording medium is provided. The apparatus includes a cleaning tank for storing therein a cleaning fluid and a gas feeding pipe, provided in the cleaning tank, for feeding a gas into the cleaning tank to generate bubbles of the gas in the cleaning fluid in which a glass substrate is immersed.

[0009] In another aspect of the present invention, a process for cleaning a glass substrate for use in information recording medium is provided. The method includes the steps of storing a cleaning fluid in a cleaning tank; immersing a glass substrate in the cleaning fluid; and feeding a gas into the cleaning tank to generate bubbles of the gas so that the bubbles are brought into contact with the glass substrate while stirring the cleaning fluid to remove deposits on the surface of the glass substrate.

[0010] Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

[0012]FIG. 1 is a front cross-sectional view of a cleaning apparatus according to one embodiment of the present invention;

[0013]FIG. 2 is a side cross-sectional view of the cleaning apparatus of FIG. 1; and

[0014]FIG. 3 is a plan view of the cleaning apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] In the drawings, like numerals are used for like elements throughout.

[0016] A sheet-form untreated glass plate is cut using a cutter made of a hardmetal or diamond to form a glass substrate in a disk form. A hole is formed in the center of the glass substrate. Examples of materials for the untreated glass plate include soda-lime glass, aluminosilicate glass, polysilicate glass, and crystallized glass, produced by a float method, a down draw method, a redraw method, or a press method. For example, a primary layer, a magnetic layer, a protecting layer, and a lubricant layer for improving the magnetic properties are formed on the surface of the glass substrate to prepare an information recording medium, such as a magnetic disk, a magneto-optical disk, or an optical disk. Further, the glass substrate is subjected to chemically reinforcing treatment to impart to the information recording medium an impact resistance and a vibration resistance as well as a heat resistance.

[0017] In the chemically reinforcing treatment, the glass substrate is immersed in a heated chemically reinforcing treatment solution. As the chemically reinforcing treatment solution, for example, a potassium nitrate solution, a sodium nitrate solution, a silver nitrate solution, or a mixture thereof can be used. It is preferred that the temperature of the chemically reinforcing treatment solution is about 50 to 150° C. lower than the distortion temperature of the material for the glass substrate. It is more preferred that the temperature of the chemically reinforcing treatment solution is about 350 to 400° C. By immersing the glass substrate in the heated chemically reinforcing treatment solution, monovalent metal ions contained in the constituents of the glass substrate, such as lithium or sodium ions, are replaced by monovalent metal ions having a larger ionic radius, such as potassium ions. A compression stress is exerted on the surface of the glass substrate in this state, so that the glass substrate is chemically reinforced.

[0018] After the chemically reinforcing treatment, molten salts or fine particles, such as dust, an abrasive material, or abrasive powder, are deposited on the surface of the glass substrate. The cleaning apparatus according to one embodiment of the present invention is used for removing these deposits.

[0019] As shown in FIG. 1, cleaning apparatus 100 has a cleaning tank 11 having a substantially rectangular box form and having an opening 11 a in its top surface. A drain pipe 27 is connected to the center portion or corner portion of the bottom wall of the cleaning tank 11. A valve (not shown) for opening or closing the drain pipe 27 is connected to the drain pipe 27.

[0020] A water feeding pipe 12 is provided on the bottom and one sidewall of the inner surface of the cleaning tank 11. The water feeding pipe 12 is connected to a water feeding pipe line 14 through a valve 13. When the valve 13 is opened, a cleaning fluid is discharged from a tip 12 a of the water feeding pipe 12 through the water feeding pipe line 14 and stored in the cleaning tank 11.

[0021] A cage 33 containing therein holders 32 is immersed in the cleaning fluid stored in the cleaning tank 11. Each holder 32 contains therein a plurality of glass substrates 31 at predetermined intervals.

[0022] Deposits, such as molten salts and fine particles, are deposited on the surface of the glass substrate 31 through an affinity, such as an ionic bonding, an intermolecular force, an electrostatic force, or a Coulomb force. The cleaning fluid is used for lowering the affinity of the deposits with the glass substrate so that the deposits may leave the surface of the glass substrate 31 with the cleaning fluid dissolving therein the deposits or entering between the surface of the glass substrate 31 and the deposits to permit the deposits to separate from the surface of the glass substrate 31. As the cleaning fluid, water can be used. Water is preferred because water can dissolve therein a molten salt and is neutral and thus does not affect the glass substrate 31 and is easily available.

[0023] General water may be used as the cleaning fluid, but, from the viewpoint of suppressing deposition of fine particles onto the glass substrate 31, it is preferred to use filtered pure water, ion-exchanged water, or ultrapure water. An alcohol, such as isopropyl alcohol (IPA), methanol, ethanol, or butanol, or a cationic, anionic, or nonionic surfactant can be added to the water in such an amount that they do not affect the surface of the glass substrate 31.

[0024] As shown in FIG. 2, an overflow portion 15 is formed at the upper end portion of the back sidewall of the cleaning tank 11 so that the overflow portion 15 protrudes from the sidewall of the tank. A drain pipe 16 is connected to the overflow portion 15. When water overflows the cleaning tank 11, the water is drained out of the tank from the drain pipe 16 through the overflow portion 15.

[0025] A plurality of gas feeding pipes 17 are disposed in parallel at predetermined intervals on the bottom surface of the cleaning tank 11. One end of each gas feeding pipe 17 protrudes outwards from the bottom of the cleaning tank 11, and is connected through a filter 120 (see FIG. 1) to a pump 140 (see FIG. 1) for feeding a gas to the gas feeding pipes 17. As the gas, it is preferred to use air because air does not affect the glass substrate 31 and is easily available. Instead of air, an inert gas, such as helium gas, neon gas, or argon gas, can be used. Air led to the gas feeding pipes 17 is fed into the cleaning tank 11 through holes 17 a, so that bubbles of air are generated in the cleaning water stored in the cleaning tank 11.

[0026] The bubbles generated from the holes 17 a in the gas feeding pipes 17 rise to the surface of the cleaning water stored in the cleaning tank 11. The bubbles are brought into contact with the glass substrates 31 contained in the holders 32 in the cage 33 to lower or eliminate the affinity of the deposits with the surfaces of the glass substrates 31.

[0027] The affinity of the deposits with the surface of the glass substrate 31 is lowered to some extent in a state such that the glass substrate 31 is immersed in water. When bubbles are brought into contact with the surface of the glass substrate 31 in this state, the bubbles, for example, break or collapse to exert on the surface of the glass substrate 31 a physical, external force to an extent that the deposits are liberated from the surface, thus removing the deposits. Further, as the bubbles are close to the water surface, the water pressure applied to the bubbles lowers. Therefore, increasing their diameters the bubbles push the water upwardly and rise up in the water so as to agitate the water, so that the water stored in the cleaning tank 11 is stirred.

[0028] It is preferred that the rate of feeding air to the gas feeding pipe 17 is about 30,000 to 110,000 cm³ per minute. When the air feeding rate is less than 30,000 cm³ per minute, there is a possibility that not enough bubbles are generated in water. On the other hand, when the air feeding rate is more than 110,000 cm³ per minute, a force generated when the bubbles are brought into contact with the glass substrate 31 may vigorously vibrates the glass substrate 31, and may cause small flaws, crazes, or breakage in the glass substrate 31.

[0029] It is preferred that the bubbles have a diameter of about 1 to 40 mm. The diameter of the bubbles can be determined by adjusting the diameter of the holes 17 a in the gas feeding pipes 17. When the diameter of the bubbles is less than 1 mm, there is a possibility that the deposits may not be satisfactorily liberated from the glass substrate, but also the water may not be satisfactorily stirred. On the other hand, when the diameter of the bubbles is greater than 40 mm, the contacting of the bubbles with the glass substrate 31 may vigorously vibrates the glass substrate 31, and may cause small flaws, crazes, or breakage in the glass substrate 31.

[0030] The filter 120 removes fine particles present in air having a particle diameter equal to or greater than a predetermined particle diameter. Therefore, it is possible to prevent such fine particles from mixing into the bubbles and being deposited onto the glass substrate 31.

[0031] It is preferred that the fine particles to be filtered by the filter 120 have a particle diameter equal to or greater than about 0.3 μm. When removing fine particles having a diameter of less than 0.3 μm by the filter 120, the filter 120 is likely to be clogged to increase the resistance of the filter 120, leading to feed not enough air to the gas feeding pipe 17. There is no particular limitation in the particle diameter of the fine particles to be filtered by the filter 120, but it may be 100 μm. The majority of fine particles larger than 100 μm float in water, and therefore they can be removed merely by immersing the glass substrates 31 in water.

[0032] An outlet 19 is formed in the lower portion of one sidewall of the cleaning tank 11, and an outlet pipe 20 is connected to the outlet 19. An inlet pipe 21 having an inlet 22 is provided at the upper portion of the opposite sidewall of the cleaning tank 11. The outlet pipe 20 and the inlet pipe 21 are connected to each other through a circulation pipe 23. The circulation pipe 23 is provided with a pump 24, a filter 25, and a heater 26. Water stored in the cleaning tank 11 is led by means of the pump 24 through the outlet pipe 20, and recycled to the cleaning tank 11 through the circulation pipe 23 and the inlet pipe 21. That is, the water stored in the cleaning tank 11 is circulated through the circulation pipe 23.

[0033] The filter 25 removes fine particles including metallic particles, dust, an abrasive material, or abrasive powder, being insoluble in water and having a particle diameter equal to or greater than a predetermined particle diameter. The action of filtration by the filter 25 maintains favorable state of cleanliness of the water stored in cleaning tank 11. It is preferred that the fine particles to be removed by the filter 25 have a particle diameter equal to or greater than about 0.2 μm. When removing fine particles having a particle diameter of less than 0.2 μm by the filter 25, the filter 25 is likely to be clogged to increase the resistance of the filter 25, leading to a danger that the cleaning effect of water is lowered. There is no particular limitation in the particle diameter of the fine particles to be removed by the filter 25, but it may be 100 μm. The majority of fine particles larger than 100 μm float in water, and therefore they can be removed merely by immersing the glass substrates 31 in water.

[0034] The heater 26 is disposed on the upstream of the filter 25. The heater 26 heats the water flowing through the circulation pipe 23 so that the warm water stored in the cleaning tank 11 is maintained at a predetermined temperature. Therefore, the glass substrate 31 is cleaned with warm water maintained at a predetermined temperature for a given period of time. After the glass substrate 31 is cleaned with the warm water for a given period of time, heating by means of the heater 26 is terminated and water is fed into the cleaning tank 11, so that the glass substrate 31 is slowly cooled.

[0035] It is preferred that the temperature of the warm water is about 20 to 70° C. When the temperature of the warm water is lower than 20° C., there is a possibility that a molten salt is hardly dissolved in the water and the detergency is lowered. When the temperature of the warm water is higher than 70° C., water is likely to evaporate and a molten salt once dissolved may be deposited again.

[0036] It is preferred that the time for cleaning the glass substrate 31 with warm water is about 30 to 60 minutes. When the warm water cleaning time is shorter than 30 minutes, deposits are not satisfactorily removed. When the warm water cleaning time is longer than 60 minutes, the cleanliness of the glass substrate 31 is not improved any more and the treatment time is merely prolonged.

[0037] The rate of circulating water by means of the pump 24 is adjusted by changing the capacity of the cleaning tank 11 and the time for cleaning with warm water. Namely, it is preferred to adjust the rate of circulating water so that the frequency of circulation of all the water stored in the cleaning tank 11 is 1 to 5 cycles in a given period of time for cleaning with warm water. Specifically, it is preferred that the rate of circulating water is {fraction (1/20)} to {fraction (1/10)} of the capacity of cleaning tank 11 per minute. For example, when the cleaning tank 11 has a capacity of 1.015 m³, the time for cleaning with warm water is 40 minutes, and 1.015 m³ of water is circulated 2.4 times in 40 minutes, the rate of circulating water is 0.06 m³ per minute, which corresponds to {fraction (1/17)} of the capacity of the cleaning tank 11 per minute.

[0038] When the frequency of circulation of water in a given period of time for cleaning with warm water is less than 1 cycle, fine particles are mixed into the water, thus making it impossible to secure a satisfactory detergency. When the frequency of circulation of water in a given period of time is more than 5 cycles, the cleanliness of the glass substrate 31 is not improved any more and the treatment time is merely prolonged. When the rate of circulating water is less than {fraction (1/20)} of the capacity of the cleaning tank 11 per minute, the water may not be satisfactorily warmed, so that a detergency cannot be fully exhibited. When the rate of circulating water exceeds {fraction (1/10)} of the capacity of the cleaning tank 11 per minute, the cleanliness of the glass substrate 31 is not improved any more and the treatment time is merely prolonged.

[0039] Next, the operation of a cleaning apparatus 100 is described below.

[0040] When using the cleaning apparatus 100, the valve 13 is opened in a state such that the two drain pipes 27 are preliminarily closed, and water is fed into the cleaning tank 11 from the water feeding pipeline 14 through the water feeding pipe 12. The feeding of water is continued until the water overflows the overflow portion 15, and then, the valve 13 is closed to store the water in the cleaning tank 11. Then, the pump 24 is operated to circulate the water stored in the cleaning tank 11 while heating the water by means of the heater 26 so that the temperature of the water stored in the cleaning tank 11 is maintained at about 20 to 70° C.

[0041] Then, the holders 32 holding the glass substrates 31 are placed in the cage 33, and the cage 33 is immersed in the warm water stored in the cleaning tank 11. Then, air is led to the gas feeding pipes 17 in a state such that the warm water is circulated, and air is fed into the warm water from the holes 17 a to generate bubbles of air in the warm water.

[0042] The bubbles generated in the warm water rise to the water surface while stirring the warm water. At this moment, the bubbles are brought into contact with the glass substrates 31, so that a physical, external force is exerted on deposits. When a physical, external force is exerted on the deposits in a state such that the affinity of the deposits with the surfaces of the glass substrates 31 is lowered by immersing the glass substrates in warm water, the affinity of the deposits with the surfaces of the glass substrates 31 is eliminated so that the deposits are liberated from the surfaces of the glass substrates 31. Among the deposits liberated from the glass substrates, a molten salt is dissolved in the warm water, and fine particles are captured by the bubbles or dispersed in the warm water.

[0043] As the bubbles rise up in water, the warm water having dissolved therein a molten salt is forced to rise to the water surface from the surfaces of the glass substrates 31. Therefore, liquid exchange always occurs on the surfaces of the glass substrates 31. When the warm water forced to rise up-reaches the surface of the warm water, the molten salt dissolved is diffused uniformly in the warm water stored in the cleaning tank 11. For this reason, no large difference is caused between the solubility of the molten salt in the vicinity of the glass substrate 31 and that in the other portions, and a uniform solubility of the molten salt can be obtained in the entire warm water stored in the cleaning tank 11, thus exhibiting a satisfactory detergency.

[0044] Fine particles are forced to rise to the water surface from the surfaces of the glass substrates 31, together with the warm water, and, when they reach the water surface, they are uniformly dispersed in the warm water stored in the cleaning tank 11. Fine particles being dispersed in the warm water and having a particle diameter equal to or greater than 0.3 μm are removed by the filter 25. Therefore, it is possible to prevent such fine particles from being deposited again on the surfaces of the glass substrates 31.

[0045] The glass substrates 31 are cleaned with the warm water for a given period of time, and then heating of water by means of the heater 26 is terminated. At this moment, water is fed from the water feeding pipe 12 in a state such that circulation of water by means of the pump 24 and feeding of air from the gas feeding pipes 17 are continued. Thus, the majority of warm water having dissolved therein a molten salt and having dispersed therein fine particles is drained out of the cleaning tank 11 through the overflow portion 15. Then, the glass substrates 31 are slowly cooled until the warm water in the cleaning tank 11 is replaced by water at room temperature. After completion of cooling the glass substrates 31, feeding of water from the water feeding pipe 12, circulation of water by means of the pump 24, and feeding of air from the gas feeding pipes 17 are stopped, and the cage 33 is taken out from the cleaning tank 11 and transferred to the subsequent step. After the cage 33 is taken out from the cleaning tank 11, the water stored in the cleaning tank 11 is drained through the drain pipe 27.

[0046] The cleaning apparatus 100 according to the present embodiment has the following advantages.

[0047] Bubbles of a gas are generated in the water stored in the cleaning tank 11, and brought into contact with the glass substrates 31 while stirring the water to remove deposits from the glass substrates. Therefore, the deposits are uniformly dispersed or dissolved in the entire water stored in the cleaning tank 11, so that a satisfactory detergency is exhibited, and further, redeposition of the deposits is suppressed. In addition, differing from the conventional ultrasonic cleaning, the bubbles uniformly spread the entire cleaning tank 11 and are almost surely brought into contact with the glass substrates 31, and therefore no deposit remains after cleaning, thus improving the efficiency of the cleaning treatment.

[0048] The water stored in the cleaning tank 11 is circulated while being heated by means of the heater 26, and therefore the water stored in the cleaning tank 11 is maintained at a predetermined temperature, making it possible to maintain a favorable detergency.

[0049] The filter 25 disposed in the circulation pipe 23 removes fine particles present in water. Therefore, redeposition of the deposits onto the glass substrates 31 is more effectively suppressed.

[0050] The bubbles of a gas have a diameter of about 1 to 40 mm. Therefore, removal of deposits and stirring of water are favorably performed while suppressing damage of the glass substrates 31.

[0051] It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms.

[0052] For example, the gas feeding pipes 17 may be disposed on both sidewalls of the cleaning tank 11 to generate bubbles of a gas not only from the bottom inner surface but also from the sidewall of the cleaning tank 11. In this case, the efficiency of stirring water is improved.

[0053] When a certain amount of warm water is stored in the cleaning tank 11, the water being circulated may be heated by means of the heater 26 while feeding water from the water feeding pipe 12. In this case, the warm water having dissolved or dispersed therein deposits is drained through the overflow portion 15 during cleaning, and hence the cleanliness of the water stored in the cleaning tank 11 is improved.

[0054] The heater 26 may be omitted and warm water may be fed from the water feeding pipe 12.

[0055] The glass substrates 31 may be irradiated with ultrasonic waves in a state such that the glass substrates 31 are immersed in the cleaning fluid stored in the cleaning tank 11. In this case, vibration caused by the ultrasonic waves pulverizes the deposits on the surfaces of the glass substrates, and thus, the cleanliness of the surfaces of glass substrates 31 is further improved by a synergistic effect of the ultrasonic waves and the bubbles.

[0056] Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims. 

What is claimed is:
 1. An apparatus for cleaning a glass substrate for use in information recording medium, the apparatus comprising: a cleaning tank for storing therein a cleaning fluid; and a gas feeding pipe, provided in the cleaning tank, for feeding a gas into the cleaning tank to generate bubbles of the gas in the cleaning fluid in which a glass substrate is immersed.
 2. The cleaning apparatus according to claim 1, wherein the cleaning tank has an inlet and an outlet for the cleaning fluid, the cleaning apparatus further comprising: a circulation pipe connecting the inlet to the outlet; a pump, provided in the circulation pipe, for circulating the cleaning fluid; and a heater, provided on the circulation pipe, for heating the cleaning fluid being circulated.
 3. The cleaning apparatus according to claim 2, wherein the heater heats the cleaning fluid being circulated so that the temperature of the cleaning fluid stored in the cleaning tank is maintained at about 20 to 70° C.
 4. The cleaning apparatus according to claim 2, wherein the pump circulates the cleaning fluid at a rate of {fraction (1/20)} to {fraction (1/10)} of the capacity of the cleaning tank per minute.
 5. The cleaning apparatus according to claim 2, further comprising: a filter, provided in the circulation pipe, for removing fine particles being present in the cleaning fluid and having a particle diameter equal to or greater than a predetermined particle diameter.
 6. The cleaning apparatus according to claim 5, wherein the filter removes fine particles having a particle diameter equal to greater than about 0.2 μm.
 7. The cleaning apparatus according to claim 1, wherein the bubbles have a diameter of about 1 to 40 mm.
 8. The cleaning apparatus according to claim 1, wherein the gas feeding pipe is one of a plurality of gas feeding pipes disposed in parallel on the bottom surface of the cleaning tank.
 9. The cleaning apparatus according to claim 1, wherein the rate of feeding the gas into the cleaning tank is about 30,000 to 110,000 cm³ per minute.
 10. The cleaning apparatus according to claim 1, further comprising: a filter, connected to the gas feeding pipe, for removing fine particles having a particle diameter equal to or greater than about 0.3 μm from the gas fed to the gas feeding pipe.
 11. The cleaning apparatus according to claim 1, wherein the cleaning fluid is water, and wherein the gas is air.
 12. A process for cleaning a glass substrate for use in information recording medium, comprising the steps of: storing a cleaning fluid in a cleaning tank; immersing a glass substrate in the cleaning fluid; and feeding a gas into the cleaning tank to generate bubbles of the gas so that the bubbles are brought into contact with the glass substrate while stirring the cleaning fluid to remove deposits on the surface of the glass substrate.
 13. The process according to claim 12, further comprising the steps of: circulating the cleaning fluid stored in the cleaning tank; and heating the cleaning fluid being circulated.
 14. The process according to claim 13, wherein the heating step includes heating the cleaning fluid stored in the cleaning tank to about 20 to 70° C.
 15. The process according to claim 13, wherein the circulating step includes circulating the cleaning fluid at a rate of {fraction (1/20)} to {fraction (1/10)} of the capacity of the cleaning tank per minute.
 16. The process according to claim 13, further comprising the step of: removing fine particles being present in the cleaning fluid being circulated and having a particle diameter equal to or greater than a predetermined particle diameter.
 17. The process according to claim 16, wherein the removing step comprises removing fine particles having a particle diameter equal to or greater than about 0.2 μm.
 18. The process according to claim 12, wherein the bubbles have a diameter of about 1 to 40 mm.
 19. The process according to claim 12, wherein the gas feeding pipe is one of a plurality of gas feeding pipes disposed in parallel on the bottom surface of the cleaning tank.
 20. The process according to claim 12, wherein the rate of feeding the gas into the cleaning tank is about 30,000 to 110,000 cm³ per minute.
 21. The process according to claim 12, further comprising the step of: removing fine particles having a particle diameter equal to or greater than about 0.3 μm from the gas fed to the gas feeding pipe.
 22. The process according to claim 12, wherein the cleaning fluid is water, and wherein the gas is air. 